Earth's Atmosphere

The word "atmosphere" (from the Greek "atmos," or breath, and "sphaira," ball) refers to the gas that surrounds any planet or star. Earth's atmosphere, which is held in place by Earth's gravity, is made up of nitrogen, oxygen, argon, carbon dioxide, small amounts of other gases, and a little bit of water vapor—in other words, what we call "air." Our atmosphere gives us a protective barrier from the sun's ultraviolet radiation and a cushion against the changing extremes of temperatures day to day.

Earth's First Layer of Air: Troposphere

Greek for "tropos," meaning turning or change.

Closest to the Earth, starting as close as just above the surface of the Earth and extending as high as 60,000 feet up, you will find the Troposphere. This is where we live everyday of our lives. Because all of the other layers are pressing down on the troposphere due to gravity, this is also the layer of Earth's atmosphere that contains the greatest amount of pressure. The majority of our weather systems are found within the troposphere, which gets colder the higher up it goes. Eighty percent (80%) of the Earth's atmosphere is found in this layer, which is why it sustains life so well, and because it also has the greatest concentration of oxygen of the five layers.

Earth's Second Layer of Air: Stratosphere

Greek for "stratus," meaning to stretch or extend.

The second layer to Earth's atmosphere is the stratosphere, which stretches out to about 160,000 feet above the Earth and contains the ozone layer, which is just about 50,000-115,000 feet above the Earth's atmosphere. The bottom part of the stratosphere has an almost constant temperature, however this layer (unlike the troposphere) gets hotter and hotter the higher it goes. You will see commercial airliners flying in the bottom part of this layer of Earth's air to avoid all of the turbulence and bad weather found in the highest parts of the troposphere.

Earth's Third Layer of Air - Mesosphere

Greek for "mesos," meaning middle.

Extending from around 160,000 feet to 285,000 feet, the mesosphere is the coldest of the five layers of Earth's atmosphere—more cold than the coldest temperature ever recorded in Antarctica (-129°F!). This freezing cold layer is the biggest protector of the Earth when it comes to meteorites: most meteors burn up when they enter this part of Earth's atmosphere. Not very much is known about the mesosphere because it begins just a little higher than the maximum altitude allowed for aircraft, but lower than the minimum altitude for rocket ships and other spacecraft. Because of the limiting factors to this layer, the mesosphere has not been explored very much at all, causing some scientist to call this layer the"ignorosphere."

Earth's Fourth Layer of Air - Thermosphere

Greek for "thermos," which means hot.

Right above the mesosphere, the thermosphere is about 285,000 feet to over 400,000 feet. This layer of Earth's air gets increasingly hotter as it goes farther away from the Earth's surface. Even though it is so very hot (temperatures can get as hot as 27,000°F!), it is ultimately empty of any matter. Because of the lack of matter here, a normal thermometer would read the temperature to be way below zero. This layer also contains the ionosphere, which is the part of the atmosphere that gets ionized by the sun's solar radiation. It is also the area where auroras like the Auroa Borealis, or "Northern Lights," are created.

Earth's Fifth Layer of Air - Exosphere

Greek for "exose," meaning outer or exterior.

This is the highest region of the Earth's atmosphere, and extends more than 6,000 miles into space. At this level, the last level before outer space, the only gases that can float this high have to be the lightest gases (mostly hydrogen, and small amounts of helium, carbon dioxide, and atomic oxygen). The density of these molecules is so low that there is rarely any chance that they will run into each other. With no collisions holding these molecules back, they are able to escape Earth's gravitational pull and gracefully drift off into outer space. The exoshpere is also where you find most of the worlds satellites to be orbiting.